The present invention relates to the handling, storing, and distribution of bulk dry materials, such as sand.
There are many applications in which it is necessary to store large amounts of bulk dry material at a site. The following description gives the background of the invention in the context of one such application—the handling, storage and distribution of silica sand used as a proppant at a gas or oil well site in carrying out the process known as hydraulic fracturing, or “fracking.” It should be understood, however, that the invention is not so limited.
The conventional prior art approach to storing sand at a well site is to place storage trailers horizontally on the ground and load and unload the sand using pneumatics. Disadvantageously, this requires a large footprint on the site, which has an impact on site lease costs and has environmental impacts as well. Other problems with this approach include inefficient use of trucking equipment, increased complexity of operations at the well site and, ultimately, lower downhole production due to proppant damage.
If, in order to ameliorate these problems, only a few storage trailers are used on site, then other issues arise. For example, having low sand capacity at the well site causes logistical problems and increases incremental costs associated with truck and rail demurrage. The loading and unloading of the sand is inefficient. And pneumatic filling changes the particles of silica sand from their generally spherical shape to irregular/broken shapes. This results in less negative space, i.e., less space between the sand particles, which leads to lower well conductivity, i.e. lower rates of extraction of the oil or other material being drilled for. Pneumatic pumping also creates an unhealthy dust.
A known alternative to the horizontal storage approach, which addresses at least some of the above problems—such as site footprint—is to store the sand vertically in free-standing silo units that can be trucked to the well site and then stood on end. The silo units are filled with sand from the top and the sand can then be gravity-drained or discharged from each silo unit through a chute extending from the side of the silo unit. Use of such free-standing silo units ameliorates some of the problems associated with the use of horizontal storage trailers.